Trypanosome alternative oxidase (TAO) is the only terminal oxidase found within the mitochondrial electron transport system in the bloodstream form (BF) of the parasite, the form that exist in the mammalian host. TAO expression is developmentally regulated in the bloodstream (BF) and procyclic forms (PF). Studies in our lab have demonstrated that TAO is regulated at the level of mRNA stability and de novo protein synthesis is required for the reduction of the mRNA pool in the PF form. In trypanosomes, gene expression is regulated post transcriptionally and the 3'- untranslated regions (UTRs) play important roles for this regulation process. TAO contains a long 3'- UTR of about 2 kilobases, and preliminary data suggest that it is most likely involved in the transcript stability in the PF. Recent evidence suggest that TAO and the cytochrome pathway protein expression are coodinately regulated, in Trypanosoma brucei. Thus, we propose here, to investigate the role of the specific regions of TAO 3'-UTR in the regulation of TAO gene expression in Trypanosoma brucei. [unreadable] [unreadable]